1. Field of the Invention
The present invention relates generally to devices for operating on wells, such as in workover operations. More specifically, the present invention relates to coiled tubing systems for injecting and extracting continuous lengths of tubing into and out of wells in various well servicing operations.
2. Description of the Prior Art
Various tubing systems are shown in the prior art for working on wells. Generally speaking, a continuous metal tubing is driven down the well bore by means of an injector head. In the prior art devices, a pair of continuous-chain tube gripping assemblies were motor driven in the injector head to grip the tubing and move it down the well bore. Reverse operation of the gripping assemblies was used to withdraw the tubing string from the well bore. At the surface, the tubing was stored on a large drum or reel from which the tubing was withdrawn by the pull of the injector head. The reel was motor driven to rewind the tubing as it was withdrawn from the well.
The prior art coiled tubing systems utilized opposing chain designs in which a plurality of gripper members were carried by the opposing chains, the grippers being frictionally driven to engage a selected length of tubing for injecting the tubing within the well bore.
The prior art designs suffered from a number of disadvantages. The opposing chain drive design could not be easily removed from the selected length of tubing being inserted within the well bore if problems occurred during the well working operation. As a result, it was usually necessary to cut the tubing at the well surface with the result being a weakened section of the tubing string. The opposing chain drive designs satisfactorily gripped smaller diameter tubing such as one inch tubing but were not well adapted for gripping larger diameter tubing. The prior art systems also required a large number of working parts which increased maintenance and operating costs. Because the opposing grippers were formed with jaw openings of fixed diameter, it was not easy to retrofit the injector head for a different size diameter of coil tubing in the field. It was also difficult to prevent wear to high dollar component parts of the prior art devices such as the fixed diameter grippers.
In Applicant's prior U.S. Pat. No. 5,133,405, issued Jul. 28, 1992, entitled "Coil Tubing Injector Unit", many of the aforementioned shortcomings were overcome. The '405 patent shows a coil tubing injector which is positioned adjacent the well bore and includes a longitudinal opening which defines a vertical run for the injector unit which is alignable with the well bore vertical axis. Gripper block assemblies are carried on the main injector frame and include plier-like halves which are pivotable between an open position and a closed, gripping position as the assemblies enter the vertical run so that the plier halves grip a selected length of tubing fed into the main injector frame along the central vertical axis of the injector unit to inject tubing into the well bore. A drive mechanism, including a chain drive, is located on the main injector frame and drives the gripper block assemblies in a continuous loop within the main injector frame.
The coil tubing injector shown in the '405 patent was able to accommodate larger diameter tubing and could be readily refitted in the field to accommodate a variety of tubing sizes. The novel injector also featured fewer moving parts and lower maintenance costs as compared to the prior art units. The new injector also featured an open face design to allow the unit to be easily removed from a string of tubing being injected into a well.
In spite of these advances, certain improvements have been made in the new injector design which allow it to operate more smoothly and quietly with less wear and tear on the gripper block assemblies and the vertical run of the main injector frame. These improvements also allow the gripper block assemblies to more firmly and securely engage the coil tubing being injected into the well bore and can more easily accommodate tubing sizing and dimensional variations. The improved design allows the gripper block assemblies to go from the unloaded to fully loaded positions within the injector frame vertical run with minimum ease.